ALIS-2 (Automatic Link Set-up) is a simplex system operating with a baud rate of 240.82 baud. ALIS-2 is described in the "Report of the CCIR 1990, Fixed Service at Frequencies below about 30 MHz" of the ITU.
|
Parameter |
Value |
|
Frequency range |
HF |
|
Operation modes |
Simplex ARQ |
|
Modulation |
MFSK-8 |
|
Symbol rate |
240.82 Bdd |
|
Receiver settings |
DATA, CW, LSB or USB |
|
Input format(s) |
AF, IF |
|
Additional Info |
ITA-5 |
ALIS-2 is 8-FSK modulated. The tone spacing is 240 Hz, and the tone duration is 4.15254 ms. The transmission block consists of 55 tri-bits, resulting in 165 bits per frame. In addition to the preamble of 21 bits, each block contains 126 data bits. The preamble includes an identification code, allowing different systems to be identified.
Two identification bits signal four operational states: traffic, idle, RQ and binary data transfer. The 16-bit CRC-checksum serves the detection of transmission errors and error correction purposes.
The overall transmission and receive cycle of ALIS-2 is 354 bits, which is equivalent to 490 ms. In case of an error-free data transmission, the terminal bit rate is 720 bit/s.
ALIS-2 almost always uses the ITA-5 ASCII alphabet.
The ALIS-2 system automatically determines the optimum operating frequency after having received a CALL command. The station then sends a synchronization word, address, block counter and a status word. The receiving station correlates this bit sequence and synchronizes itself. If the transmission link is interrupted, ALIS-2 will search for a new frequency to re-establish the link.
If an ALIS-2 system is identified the status line will display System: “XXXXXXXXh", where XXXXXXXXh denotes an eight digit hex id string.